Since the first protocols for sending packetized data over networks were established, many have endeavored to send packetized voice signals over the same network infrastructure. The challenge has not been whether voice signals can be sent in packetized format, but rather whether packetized voice signals can be sent reliably and of equivalent quality to that of traditional switch-based telephone systems, all at a price that is cost-competitive with these traditional telephone systems.
The general view has been that because voice signals require real-time transmission, voice communications must have a "guaranteed" bandwidth channel as in traditional switch-based telephone systems in order to provide the desired quality of service. This view has led to the creation of protocols (e.g., Asynchronous Transfer Mode (ATM) and IsoEthernet) that provide virtual, dedicated channels for voice and other real-time applications and a separate virtual data channel. Networks that implement these protocols are expensive. These high costs have limited the growth of the installed base of these products. The most affordable and the most dominant network protocol is standard (IEEE 802.3) 10BaseT Ethernet, which does not provide a virtual guaranteed bandwidth channel. The large installed base of 10 MBit Ethernet has created an incentive for the development of improved Ethernet protocols, such as 100 MBit, 1 GBit and switched Ethernet, all with backward compatibility for 10 MBit Ethernet.
For many years, the communications industry has been interested in using a data network infrastructure to carry voice (or audio) signals. There are several reasons for this interest. In general, it is less expensive and less complicated to offer telephony, messaging and computer integration over a single network infrastructure than over separate infrastructures. By sending voice over the data network, it is possible to merge the functionality of advanced telephone systems with the power, scaleability and open connectivity of networking solutions.
It has been known in the communications industry for many years that computer-based applications can be used to increase the functionality of telephone systems. For example, an entire industry has been created to develop and sell personal computer (PC) based applications that increase the efficiency of telephone call centers. The PC has also been used as voice messaging platform. Finally, several companies have developed complete telephone systems by building telephone switching hardware into the network server. A typical configuration of such a system includes ISA bus cards connected via a separate telephony bus (e.g., the signal computing system architecture (SCSA) bus and the multi-vendor interpolation protocol (MVIP) bus) to provide both telephone station connections and central office (CO) telephone connections. In each of these cases, the computer network and the telephone network remain separate, but they are linked using hardware and software tie-ins from the PC or network server to either the desktop telephone or to the telephone system switch.
In contrast, sending packetized voice over the same network infrastructure as packetized data eliminates the need for two infrastructures and makes it possible to take advantage of advanced computer telephony and PC messaging applications running on the data network without the expense of hardware and software links. Another well-known advantage of packetized voice (or audio) is the ability to transfer signals over wide area network infrastructures (e.g., the Internet) as a means of saving on toll charges for telephone usage. Various products have been introduced to send packetized audio over the Internet, in particular. Some of these products include accessories that interface with the Private Branch Exchange (PBX) to enable the time-division multiplexed digital signal to be converted into a packet-based digital signal.
In summary, the advantages of sending voice and data over the same infrastructure have been recognized for some time. Several companies have discussed systems that operate both the voice and data communications over the same network infrastructure (i.e., one wire for both voice and data). The challenge has been to provide quality of service for voice and other applications that need real-time bandwidth even when a network is heavily loaded with data traffic, and to do so in a cost-effective manner.